Picture projector

ABSTRACT

A motion picture projector for use especially in teaching machines in continuous engagement with the film, which is stepped ahead selectively in different projector modes - i. e., motion picture, slow motion, still picture, single frame-to-frame and is driven continuously at fast speed in different scan modes. The step movement of the sprocket wheel is produced by a high speed cam-actuated pawl and ratchet mechanism through a one revolution spring clutch, and scanning movement is produced by a separate drive motor in continuous coupling engagement with the sprocket wheel. By special design great indexing accuracy and quiet operation are achieved.

United States Patent 1 [111 3,709,417

Brill 51 Jan. 9, 1973 [54] PICTURE PROJECTOR [75] Inventor: Henry L.Brill, Flushing, NY. Primary Exami"er Rld 'al:d Schacher Attorney-GeorgeH. Fritzlnger [73] Assignee: E. R. E. Laboratory, Inc., West Orange, 57ABSTRACT [22] Filed: June 1971 A motion picture projector for useespecially in [21] APPL 148,403 teaching machines in continuousengagement with the film, which is stepped ahead selectively indifferent projector modes i. e., motion picture, slow motion,

[52] [1.5. Ci. ..226/76, 226/145, 226/157, Sti" picture, single frame toframe and is driven com [51] I t Cl G0 3 b l tinuously at fast speed indifferent scan modes. The

ll Step movement of the sprocket wheel is produced by a [58] Field OfSearch ..226/76, 157, 144, 145; g speed canbactuated p and ratchetmechanism 352/187 188 through a one revolution spring clutch, andscanning movement is produced by a separate drive motor in [56]References C'ted continuous coupling engagement with the sprocket UNITEDSTATES PATENTS wheel. By special design great indexing accuracy andquiet operation are achieved.

2,040,856 5/1936 Krum ..226/l57 X 3,075,680 1/1963 Bolinder ..226/ 15714 Claims, 9 Drawing Figures PATENTED JAN 9 I973 SHEET 1 BF 6PATENTEDJAN 9 I975 SHEET 2 0F 6 INVENTOR. HENRY L. BRILL AGENTPATENTEUJAM 9197s 7 3.709.417

' SHEET 3 [IF 6 [NV 1 FOR. HENRY L. RILL AGENT PATENTEBJAN 9191s3,709,417

SHEET u m5 L I FIG.'6

49 M it 50 I N VENTOR.

HENRY L. BRILL AGE/VT PATENTEDJAI 9 I973 SHEET 5 0F 6 V -Em I= INVENTOR.HENRY L. BRILL AGENT PICTURE PROJECTOR It is an object of the inventionto provide a simplified drive mechanism for a motion picture projectorwherein a stepping movement of the film and a continuous scanningmovement thereof are both accomplished through a sprocket wheel incontinuous engagement with the film.

Another object is to drive the sprocket wheel with a step movement inall projector modes by a cam operated pawl and associated ratchet wheelwherein the rocker lever for the pawl comes into positive interlockingengagement with the ratchet wheel at the end of each step advance andthe ratchet wheel is restrained by a damping drum to achieve accurateindexing.

Another object is to reduce the masses of the moving parts of theratchet mechanism to a minimum and to activate the rocker lever at itscenter of percussion to reduce vibration and noise during all projectormodes.

Another object is to provide an improved pawl and ratchet mechanism thatwill enable each step advance of the film to be achieved at such highspeed that the motion of the film is imperceptible and the need for ashutter is eliminated.

A further object is to provide such projector with a reversible scanmotor in permanent coupling with the sprocket wheel.

A still further object is to provide a solenoid operated shift mechanismwhich converts the drive mechanism instantaneously from projector modesto scanning modes.

These and other objects of the invention will be apparent from thefollowing description and the appended claims.

In the description of my invention reference is had to the accompanyingdrawings, of which:

FIG. 1 is a top plan view of a motion picture projector incorporating myinvention;

FIG. 2 is a front elevational view of the projector;

FIG. 3 is a left-hand elevational view; FIG. 4 is a section on the line4-4 of FIG. 2; FIG. 5 is a section on the line 5-5 of FIG. 1; FIG. 6 isa section on the line 6-6 of FIG. 1; FIG. 7 is a section on the line 77of FIG. 1; FIG. 8 is a section on the line 88 of FIG. 7; and FIG. 9 is asimplified block diagram of the drive circuitry for the projector.

The projector mechanism has a frame comprising a base plate 10 to theright end portion of which is bolted an L-bracket 11 supporting a drivemotor 12. On the shaft of the motor there is a drum type cooling fan 13and a pulley 14. The pulley is coupled by a belt I5 to a pulley l6 on acam shaft 17. This shaft extends from right to left along the front ofthe projector and is journaled in a standard I8 near its right end andin a stan dard 19 at its left end both upstanding from a separateintermediate base 20. (FIG. 2). The standards 18 and I9 and the separatebase 20 form an adjustable frame for the projector mechanism hereinafterfurther described. At the left and right sides of the adjustable frameare standards 21 and 22 secured by screws 23 to the main base I0 (FIGS.3 and 5). These standards are interconnected by a tie bar 24intermediate the height of the standards. Pivot studs 26 and 27 traversethe fixed standards 21 and 22 and thread into the side standards l9 andI8 of the adjustable frame for pivotally supporting the latter at thefront of the projector. A cam block 87 is provided for tilting the frame18-20 about these studs to adjust the framing of the film as is hereinlater more fully described.

In the rearward left half portion of the projector there is a filmcartridge 28 preferably of an endless film type such as is described inthe pending Walker application Ser. No. 86,076, filed Nov. 2, 1970. Thiscartridge has a flat forward wall 29 provided with a wide rectangularopening 30. The cartridge is mounted from the rear of the projector in astandard type holder 31 which is mounted on a platform 32 (FIG. 5)secured rigidly to the main base 10. The holder has an upright frontwall 33 (FIGS. 1 and 2) provided with a lens aperture 34 and a slot 35for enabling a sprocket wheel 36 to engage the sprocket holes 37 in ashort length of the film. A lamp 38 mounted also on the platform 32 ispositioned to direct light obliquely into the hollow portion of thecartridge whereat it is reflected by a mirror (not shown) through thelens aperture 34. The mirror is shiftable into and out of the holder asafter the cartridge is mounted and before the same is removed by turninga control knob K shown in FIG. 2.

The sprocket wheel 36 is mounted on a shaft 39 journaled at its left endin the standard 19 and at its right end in an intermediate standard 40upstanding from the adjustable base 20, the two standards beinginterconnected by a tie bar 41 shown in FIG. 1. Secured to the left endportion of the shaft 39 near the standard 19 is a ratchet wheel 42 andsecured to the shaft to the right of the sprocket wheel 36 is a pulley43. A scan motor 44 is mounted on the intermediate standard 40 and iscoupled via a belt 45, step-down pulley 46 and belts 47 to the pulley 43to provide a permanent coupling of the scan motor to the sprocket wheel.Further, secured to the shaft 39 at the right of the intermediatestandard 40 is a star wheel 48 engageable by a stop pawl 49 shown inFIGS. 1, 5 and 6. This pawl is pivoted at 50 to the standard 40 and isbiased into disengaged position by a tension spring 51. By activation ofa solenoid 52 the pawl is pushed into engagement with the star wheel tobrake the drive of the shaft 39 and stop the film at an exact pointwherein a frame of the film is at the lens aperture 34.

A cam 25 on the left end portion of the shaft 17 operates against aroller 53 journaled on a nearly vertical rocker lever 54 pivoted at itslower end on a stud 55 secured to the standard 19 and biased via spring56 towards the cam (FIGS. 2 and 4). The rocker lever 54 is disposedbetween the cam 25 and the ratchet wheel 42, and has a nearly horizontalpawl 57 pivoted at 58 to its upper end portion. The pawl 57 engages theupper or crest portion of the ratchet wheel 42 relative to the pivot 55of the rocker lever under pressure of a tension spring 59 connectedbetween the pawl 57 and lever 54. Above the rocker lever 54 there is aone-way latch spring 60 mounted at one end on a bracket 61 secured tothe standard 19. This latch spring is biased to engage the ratchet wheel42. At the end of each forward stroke of the rocker lever 54 the latchpawl snaps over a tooth 42a of the ratchet wheel to latch the ratchetwheel against reverse movement during the return stroke of the rockerlever.

Each advance of the rocker lever 54 and each step advance of the ratchetwheel 42 is limited by an interlocking engagement of a pair of teeth 120and 121 on the rocker lever 54 respectively with a tooth 42b and a pairof teeth 42c and 42d of the ratchet wheel. The tooth 120 has a widthabout one-half the inter-tooth space on the ratchet wheel and ispositioned to engage the leading face of the tooth 42b approximately ona diameter line of the ratchet wheel in tangency with the line of travelof the tooth 120. The tooth 121 engages the next inter-tooth space42c42d and has a width sufficient to engage that space without play. Inorder that the rocker lever may engage the ratchet wheel progressivelyduring the latter position of each advance stroke the leading half ofthe tooth 121 is stepped back at 121a by half the depth of eachinter-tooth space on the ratchet wheel.

The cam shaft 17 is driven from the pulley 16 through a one-revolutionspring band clutch 62 shown in detail in FIG. 8. The pulley 16 is freelyjournaled on the shaft 17 against a collar 63 pinned at 64 to the shaft.The collar and pulley have hubs 16a and 63a abutting end to end and ofequal diameters. On these hubs there is a coil spring 65 surrounded byan outer sleeve 66 to prevent any deformation of the spring. The coilspring has a tail 65a at one end anchored in the collar and has a radialtang 65b at the other end. An armature 67 of an electromagnet 68 isnormally in a latching position against the tang 65b as shown in FIG. 5to allow the pulley to be driven in a counterclockwise direction withslippage in the coil spring. However, the instant the electromagnet isemergized to unlatch the tang 67, the coil spring grips the hub 16a bythe resilience of the spring and additionally by the friction of the hubagainst the spring to lock the pulley to the collar 63. When theelectromagnet is deenergized the armature 67 is returned to latch thetang 6512 at the end of the revolution then underway and stop the shaft17. If the electromagnet is continued to be energized it will allow themotor 12 to continue to drive the cam shaft. Each revolution of the camshaft causes the pawl 57 to advance the ratchet wheel 42 by a one-toothdistance and the film by one frame. When the electromagnet 68 isdeenergized it always stops the cam shaft 17 in the same position whichis a position wherein the rocker lever 54 is in a fully retractedposition shown in FIG. 4.

In the present projector the cam shaft 17 is driven at a high speed suchthat each revolution takes place within about 50 milliseconds. Further,a steep lobe is provided on the cam rising to its height within about30, therefore causing the ratchet wheel to be advanced by one stepwithin about 5 milliseconds. For example, if the sprocket wheel 36 hasthe same number of teeth as the ratchet wheel and each tooth representsa frame on the film, then each frame is advanced into the lens aperturewithin the 5 millisecond pull down rate of the film. This pull downspeed is the same regardless of whether the lilm is advanced by a singleframe or is stepped in sequence by a number of frames. In all cases thespeed of pull down is so high as to render the motion of the film fromone frame to the other almost imperceptible and to make unnecessary theuser of the usual shutter.

The instant a frame reaches the lens aperture the latching spring 60engages the next tooth 42a of the ratchet wheel to lock the sprocketwheel against receding movement. The lobe of the cam is about 90 longcausing the pawl to dwell in its advance position for about 15milliseconds. During the rest of the continuing revolution of the camthe pawl 57 is retracted to a position back of the next tooth as shownin FIG. 4.

In order to prevent inertia overthrow of the sprocket wheel 36 duringits fast step advance by the cam 25, the sprocket wheel shaft 39 isplaced under a friction load by a damping mechanism 69 (FIGS. 1 and 3)comprising a drum 70 secured to the shaft 39 to the left of the standard19 and a pair of diametrically opposite brake shoes 71 and 72 mountedrespectively on levers 73 and 74 pivoted at 75 and 76 to the standard 19and biased towards each other by an interconnecting tension spring 77 todraw the brake shoes against the drum.

Mounted on the upper part of the standard 19 is a scan solenoid 78 ofapusher type. The armature of this solenoid is pivoted at 79 to ahorizontal lever 80 which overlies the brake shoes 71 and 72 and ispivoted at 81 to the standard 19. Pivoted to the lever 80 is a dependingwedge 82 which engages between the two brake shoes to pry the shoesapart from the drum 70 when the solenoid 78 is activated against theaction of a return spring 83. Also, as the lever 80 is so pusheddownwardly by the solenoid, a side lug 84 thereon, which extends througha window 85 in the standard 19, is moved against a rear arm 57a of thepawl 57 first to disengage the pawl from the ratchet wheel 42 and nextto swing the pawl against the latch spring 60 to disengage it also fromthe ratchet wheel, thus freeing the ratchet wheel for movement in eitherdirection. At the end of the forward stroke of the solenoid 78 itactivates a directional start circuit 86 for the scan motor 44.

The film F is provided with a stop code 96 at the left side of thepicture frames (FIG. 9) which is a home code to which the film isadvanced whenever a home switch 97 is depressed. Further, the film isprovided with stop codes 98 on the right side of the picture frames torepresent the start positions of respective items of information such asof chapters. The codes 96-98 are detected by respective photocells 99and 100 which feed into a decoder 101. This decoder has two outputcircuits 102 and 103 which are connectable selectively by a switch 104into a stop code reader 105 to read respectively the left and rightcodes on the film.

At the start of operation of the projector a main onoff switch S isclosed to connect a 12 volt voltage source 106 to the main drive motor12. As before described, this motor drives the cooling system for theprojector'and provides the power for advancing the v film step-by-stepby the ratchet mechanism.

When the home switch 97 is closed a first pole thereof connects a 12volt voltage source 106 to the S input of a flip-flop circuit 107 and atthe same time a second pole 97a thereof connects the voltage source 106to the directional start circuit 86. The flip-flop circuit 107 istoggled to activate the scan solenoid 78 via a lead 108 and the latteractivates the directional start circuit 86 which is normally in reverseposition into its forward position to start the scan motor 44 in aforward direction. When the start circuit 86 is activated into a forwarddirection it shifts the code selector switch 104 to the circuit 102 viaan intercoupling indicated by the tie line 109 to place the detectorsystem in condition to read only the home code 96 on the left side ofthe film.

When the home code is reached the stop code reader 105 resets theflip-flop circuit 107 causing the scan solenoid 78 to be deactivated andmomentarily causing activation of the scan stop solenoid 52 via acircuit 110 and pulsing timer l1 1 for a 50 millisecond interval. Theresetting of the scan solenoid 78 cuts power off from the scan motor 44,restores the brake 69 and reengages the pawls 57 and 60 with the ratchetwheel 42; concurrently, the pulse operation of the stop solenoid 52engages the pawl 49 momentarily with the star wheel 48 to bring thesprocket wheel 36 to an immediate stop.

When a visual repeat switch 112 is depressed it starts the scan systemthe same as described above but in a reverse direction because power isnot now sent to the directional start circuit 86 leaving it in itsnormal reverse position. The code selector switch 104 is therefore leftin contact with code output circuit 103 to leave the detector system incondition to detect only the stop codes 98 on the right side of thefilm. The scan motor therefore runs in a reverse direction until a stopcode 98 is reached, at which time the scan solenoid 78 is deactivated,the stop scan solenoid 52 is momentarily activated and the film isstopped at the stop code position. Since the flip-flop circuit 107activates alternately the scan solenoid 78 and the stop solenoid 52 anypossible simultaneous operation of these two solenoids which could causemechanical interference is avoided.

Whenever the machine is not in scan condition a switch 113 controlled bythe scan solenoid 78 is closed at pole A to cause 12 volts to beconnected to the S input of a flip-flop circuit 114 when a manualnormalmotion" switch 115 is depressed. The flip-flop circuit 114 isthereby toggled and activates the solenoid 68 to engage the free runningclutch 62 and cause the film to be stepped ahead by the ratchetmechanism at a rate of about 18 frames per second i.e., the speed ofrotation of the shaft 17. Since the scan mechanism is not now operatedthe detecting system is connected to read the stop codes at the rightside of the film. When the stop code reader 105 receives a signal from astop code 98 it feeds a signal via a circuit 117 into the R terminal ofthe flip-flop circuit 114 to reset the flip-flop circuit 114 and causethe solenoid 68 to drop out and stop the step advance of the film.

A speed control 116 connected to the flip-flop circuit 114 is operableto release the clutch 62 within 50 milliseconds to stop the drive aftereach frame advance and to reactivate the clutch within a variable timelimit determined by the setting of the control so that a variable timespacing is provided between successive step movements of the film. Inthis way the projection rate can be varied from 22 frames per seconddown to a slow rate ofonc frame every second or two.

When it is desired to advance the film by a single frame a manual switch119 is depressed to connect the voltage source 106 through a pulsetiming circuit 120 direct to the solenoid 68 but this connection is madethrough the switch 113 pole B controlled by the scan solenoid 78 so thatthe ratchet mechanism cannot be operated to step the film ahead when thescan system is in operation. The momentary activation of the solenoid 68releases the clutch 62 but for a lesser time than the 50 millisecondone-revolution period of the clutch to limit the advance to a singleframe.

Since the film is driven in both its projector modes and scan modes bythe sprocket wheel 36, the sprocket wheel is left engaged with the filmcontinuously as long as the film cartridge is in its holder, thusavoiding possible damage to the film if the usual intermittentlyengageable stepping claw were used or if a claw and sprocket wheel wereused alternately. Further, the use of a sprocket wheel for all modespermits a simpler design of the projector mechanism. I

Features of the present film drive mechanism which enable a greatindexing accuracy and quiet operation to be achieved with the use of ahigh speed ratchet mechanism reside in (1) driving the cam rocker lever54 by means operating at the center of percussion of the rocker lever,(2) in engaging the ratchet wheel positively with an interlocking toothon the rocker lever 54 at the end of each advantage step, whichengagement limits the advance of the ratchet wheel to a one-toothdistance and also acts as a stop against inertia overthrow of the rockerlever limiting the advance of the pawl to a definite length, and (3) inproviding a damping drum on the ratchet wheel shaft to reducetransmission of shocks to the sprocket wheel and to hold the sprocketwheel steady during that part of each cycle when the locking tooth isnot engaged. Further, to reduce vibration and noise, the masses of thepawl 57 and rocker lever 54 are kept at a minimum to which end therocker lever is made of two thin side levers staked together in spacedparallel relation.

The aforementioned adjustability of the intermediate frame 18-20 for thepurpose of shifting the loop portion of the film engaged by the sprocketwheel 36 for framing the film in relation to the lens aperture 34comprises the cam block 87 slidably mounted on the main base 10 in aguideway 88 provided in the platform 32. The cam block has awedge-shaped finger 89 at its forward end underlying the rearwardportion of the base 20. Two bolts 90 traverse the base 20 at its leftand right rearward corners (FIG. 1) and thread into the main base 10,and between the heads of these'bolts and the base 20 are compressionsprings 91 (FIG. 4) which hold the base 20 firmly against thewedge-shaped finger 89. An adjusting screw 92 threads into the cam block87 from its rearward end and extends through a standard 93 secured tothe base 10. A collar 94 on the screw at the front side of the stud 93and a knob 95 secured to the screw at the back of the stud serve to holdthe screw from longitudinal displacement with the result that when theknob 95 is turned the cam block is shifted forwardly or rearwardly tovary the tilting of the frame 18-20 about the studs 26 and 27 and thusto shift the film relative to the lens aperture by reason of itsengagement with the sprocket wheel 36 carried by the frame 18-20.

The embodiment of my invention herein particularly shown and describedis intended to be illustrative and not necessarily limitative of myinvention since the same is subject to changes and modifications withoutdeparture from the scope of my invention, which 1 endeavor to expressaccording to the following claims.

I claim:

1. A picture projector including a picture film having successive framesand sprocket holes along the film, a sprocket wheel engaging said film,and means for intermittently advancing said film by steps comprising aratchet wheel coupled to said sprocket wheel, a rocker lever pivoted onan axis spaced from the axis of said ratchet wheel for movement of anear-end portion towards and away from said ratchet wheel substantiallyalong a diameter line of the ratchet wheel, a drive pawl pivoted to saidnear-end portion of said rocker lever for engaging an outer end portionof said ratchet wheel relative to the pivot axis of the rocker lever toadvance said ratchet wheel as the rocker lever is moved towards theratchet wheel, and a tooth on said rocker lever for engaging aninter-tooth space of the ratchet wheel on a diameter line thereof tostop said rocker lever and limit each step advance of the ratchet wheelto the distance between successive teeth.

2. The picture projector set forth in claim 1 wherein said tooth islocated on said rocker lever to engage the leading face of a tooth ofsaid ratchet wheel when said pawl has advanced said ratchet wheel by aone-tooth distance.

3. The picture projector set forth in claim 2, including a second toothon said rocker lever engageable with the next inter-tooth space on theratchet wheel ahead of that engaged by said first mentioned tooth assaid ratchet wheel is advanced by a one-tooth distance by said pawl,said second tooth being dimensioned to engage said inter-tooth space ofthe ratchet wheel without play.

4. The picture projector set forth in claim 3 wherein said firstmentioned tooth is dimensioned to engage a trailing predeterminedportion of an inter-tooth space of said ratchet wheel, and wherein saidsecond tooth is stepped along its leading half portion whereby to permitsaid first mentioned tooth and said second tooth to engage progressivelythe respective inter-tooth spaces of said ratchet wheel as the ratchetwheel is advanced through the latter portion of each one-tooth distance.

5. A picture projector including a picture film having successive framesand sprocket holes along the film, a sprocket wheel engaging said film,and means for intermittently advancing said film by steps comprising aratchet wheel coupled to said sprocket wheel, a rocker lever pivoted formovement of a portion thereof towards and away from said ratchet wheel,a drive pawl pivoted to said rocker lever for engaging said ratchetwheel to advance the latter by a one tooth distance as the rocker leveris moved towards the ratchet wheel, a rotatably mounted cam foradvancing said rocker lever during a portion of each revolution of thecam and a damping drum coupled to said ratchet wheel for imposing afriction load on the ratchet wheel to prevent inertia overthrow of theratchet wheel as it is stepped ahead by said pawl.

6. The picture projector set forth in claim 5 including spring meansconnected to said pawl for biasing it into engagement with said ratchetwheel, spring means biasing said rocker lever towards said cam, meansfor stopping said cam in a retracted position of said rocker lever, andmeans operable against said drive pawl to hold the pawl disengaged fromsaid ratchet wheel to permit unrestricted scanning movement of saidsprocket wheel in either direction.

7. The picture projector set forth in claim 6 including a one-way latchspring engaging said ratchet wheel to permit only step advance by saiddrive pawl, and means for disengaging said latch spring as said drivepawl is disengaged.

8. The picture projector set forth in claim 7 including a reversiblescan motor coupled to said sprocket wheel for driving the sprocket wheelin either direction, and a solenoid activatable for releasing saiddamping drum,

disengaging said drive pawl and latch spring and forstarting saidreversible scan motor.

9. The picture projector set forth in claim 8 wherein said scan motor iscontinuously coupled to said ratchet wheel.

10. The projector set forth in claim 9 including a star wheel coupled tosaid ratchet wheel, a latch pawl engageable with said star wheel to stopscanning movement of said sprocket wheel in either direction, and meansoperative as an incident to a momentary engagement of said latch pawlwith said star wheel to return said latch spring and drive pawl intoengagement with said ratchet wheel.

11. A picture projector including a picture film having successiveframes and respective sprocket holes, a

sprocket wheel continuously engaging said film, and

means for moving said film by said sprocket wheel in both projection andscan modes including a drive pawl and ratchet mechanism for advancingsaid sprocket wheel by steps and a scan motor coupled to said sprocketwheel for driving said sprocket wheel continuously in either direction,a rotatable cam for reciprocating said pawl and a drive motor andonerevolution clutch coupling said drive motor to said cam, and modecontrol means activatable for shifting said drive pawl out of operativeengagement with said ratchet wheel, starting said scan motor anddisabling said one revolution clutch.

12. The picture projector set forth in claim 11 including a star wheelsecured to the shaft of said sprocket wheel having as many teeth as saidsprocket wheel, a stop pawl engageable selectively with said star wheelto stop said film at any selected positioning of the film relative tosaid lens aperture, a solenoid for engaging said stop pawl with saidstar wheel, and means rendered operative as said scan motor is startedfor disabling said solenoid.

13. The picture projector set forth in claim 12 including meanseffective upon deactivating said mode control means for (1) cutting offthe power supply to said scan motor, (2) engaging momentarily said stoppawl with said star wheel to stop said sprocket wheel, and (3)reengaging said drive pawl with said ratchet wheel, restoring said brakedrum and reabling said onerevolution clutch and said solenoids.

14. in a motion picture projector including a picture film havingsuccessive frames and sprocket holes along the film and an aperturewindow through which the successive frames are projected: thecombination of a sprocket wheel engaging said film, a ratchet wheel cou-I plcd to said sprocket wheel, a rocker l'ever pivoted for movementtowards and away from said ratchet wheel, a drive pawl pivoted to saidrocker lever for engaging said ratchet wheel to advance the sprocketwheel by a one tooth distance and said film by one frame during v eachreciprocation of said rocker lever, a rotatably mounted cam forproducing one reciprocation of said rocker lever during each revolutionof movement of the cam, and means for selectively rotating said cam byintegral numbers of revolutions including a rotation drive shaft, aone-revolution integrating clutch coupling said shaft to said cam, saidclutch including a latch member returned, and means responsive to a codesignal on said film when a predetermined frame on the film reaches saidaperture window for returning said latch member to stop said film withsaid frame at said window.

1. A picture projector including a picture film having successive framesand sprocket holes along the film, a sprocket wheel engaging said film,and means for intermittently advancing said film by steps comprising aratchet wheel coupled to said sprocket wheel, a rocker lever pivoted onan axis spaced from the axis of said ratchet wheel for movement of anear-end portion towards and away from said ratchet wheel substantiallyalong a diameter line of the ratchet wheel, a drive pawl pivoted to saidnear-end portion of said rocker lever for engaging an outer end portionof said ratchet wheel relative to the pivot axis of the rocker lever toadvance said ratchet wheel as the rocker lever is moved towards theratchet wheel, and a tooth on said rocker lever for engaging aninter-tooth space of the ratchet wheel on a diameter line thereof tostop said rocker lever and limit each step advance of the ratchet wheelto the distance between successive teeth.
 2. The picture projector setforth in claim 1 wherein said tooth is located on said rocker lever toengage the leading face of a tooth of said ratchet wheel when said pawlhas advanced said ratchet wheel by a one-tooth distance.
 3. The pictureprojector set forth in claim 2, including a second tooth on said rockerlever engageable with the next inter-tooth space on the ratchet wheelahead of that engaged by said first mentioned tooth as said ratchetwheel is advanced by a one-tooth distance by said pawl, said secondtooth being dimensioned to engage said inter-tooth space of the ratchetwheel without play.
 4. The picture projector set forth in claim 3wherein said first mentioned tooth is dimensioned to engage a trailingpredetermined portion of an inter-tooth space of said ratchet wheel, andwherein said second tooth is stepped along its leading half portionwhereby to permit said first mentioned tooth and said second tooth toengage progressively the respective inter-tooth spaces of said ratchetwheel as the ratchet wheel is advanced through the latter portion ofeach one-tooth distance.
 5. A picture projector including a picture filmhaving successive frames and sprocket holes along the film, a sprocketwheel engaging said film, and means for intermittently advancing saidfilm by steps comprising a ratchet wheel coupled to said sprocket wheel,a rocker lever pivoted for movement of a portion thereof towards andaway from said ratchet wheel, a drive pawl pivoted to said rocKer leverfor engaging said ratchet wheel to advance the latter by a one toothdistance as the rocker lever is moved towards the ratchet wheel, arotatably mounted cam for advancing said rocker lever during a portionof each revolution of the cam and a damping drum coupled to said ratchetwheel for imposing a friction load on the ratchet wheel to preventinertia overthrow of the ratchet wheel as it is stepped ahead by saidpawl.
 6. The picture projector set forth in claim 5 including springmeans connected to said pawl for biasing it into engagement with saidratchet wheel, spring means biasing said rocker lever towards said cam,means for stopping said cam in a retracted position of said rockerlever, and means operable against said drive pawl to hold the pawldisengaged from said ratchet wheel to permit unrestricted scanningmovement of said sprocket wheel in either direction.
 7. The pictureprojector set forth in claim 6 including a one-way latch spring engagingsaid ratchet wheel to permit only step advance by said drive pawl, andmeans for disengaging said latch spring as said drive pawl isdisengaged.
 8. The picture projector set forth in claim 7 including areversible scan motor coupled to said sprocket wheel for driving thesprocket wheel in either direction, and a solenoid activatable forreleasing said damping drum, disengaging said drive pawl and latchspring and for starting said reversible scan motor.
 9. The pictureprojector set forth in claim 8 wherein said scan motor is continuouslycoupled to said ratchet wheel.
 10. The projector set forth in claim 9including a star wheel coupled to said ratchet wheel, a latch pawlengageable with said star wheel to stop scanning movement of saidsprocket wheel in either direction, and means operative as an incidentto a momentary engagement of said latch pawl with said star wheel toreturn said latch spring and drive pawl into engagement with saidratchet wheel.
 11. A picture projector including a picture film havingsuccessive frames and respective sprocket holes, a sprocket wheelcontinuously engaging said film, and means for moving said film by saidsprocket wheel in both projection and scan modes including a drive pawland ratchet mechanism for advancing said sprocket wheel by steps and ascan motor coupled to said sprocket wheel for driving said sprocketwheel continuously in either direction, a rotatable cam forreciprocating said pawl and a drive motor and one-revolution clutchcoupling said drive motor to said cam, and mode control meansactivatable for shifting said drive pawl out of operative engagementwith said ratchet wheel, starting said scan motor and disabling said onerevolution clutch.
 12. The picture projector set forth in claim 11including a star wheel secured to the shaft of said sprocket wheelhaving as many teeth as said sprocket wheel, a stop pawl engageableselectively with said star wheel to stop said film at any selectedpositioning of the film relative to said lens aperture, a solenoid forengaging said stop pawl with said star wheel, and means renderedoperative as said scan motor is started for disabling said solenoid. 13.The picture projector set forth in claim 12 including means effectiveupon deactivating said mode control means for (1) cutting off the powersupply to said scan motor, (2) engaging momentarily said stop pawl withsaid star wheel to stop said sprocket wheel, and (3) reengaging saiddrive pawl with said ratchet wheel, restoring said brake drum andreabling said one-revolution clutch and said solenoids.
 14. In a motionpicture projector including a picture film having successive frames andsprocket holes along the film and an aperture window through which thesuccessive frames are projected: the combination of a sprocket wheelengaging said film, a ratchet wheel coupled to said sprocket wheel, arocker lever pivoted for movement towards and away from said ratchetwheel, a drive pawl pivoted to said rocker lever for engaging saidraTchet wheel to advance the sprocket wheel by a one tooth distance andsaid film by one frame during each reciprocation of said rocker lever, arotatably mounted cam for producing one reciprocation of said rockerlever during each revolution of movement of the cam, and means forselectively rotating said cam by integral numbers of revolutionsincluding a rotation drive shaft, a one-revolution integrating clutchcoupling said shaft to said cam, said clutch including a latch memberand a single cooperating catch element for normally holding the clutchdisengaged and for engaging the clutch responsive to a release of saidlatch member and for disengaging the clutch within the revolution of theshaft then underway when said latch member is returned, and meansresponsive to a code signal on said film when a predetermined frame onthe film reaches said aperture window for returning said latch member tostop said film with said frame at said window.